feat: improve caching

templates/nix-gitlab-ci.yml

@@ -4,28 +4,53 @@ spec:
       type: string
       description: "latest | latest-cachix | latest-attic etc."
       default: latest
+    cache_files:
+      type: array
+      description: |
+        Files to use as the cache key for the generated pipeline yaml.
+        If you use "ci.nix" to define CI, add that here for example
+      default: ["flake.nix", "flake.lock"]
+    disable_cache:
+      type: string
+      description: |
+        Disables any caching provided by this component. Set to any non-empty value to disable caching.
+      default: ""
 ---
-
 stages:
   - build
   - trigger
-
+variables:
+  NIX_CI_DISABLE_CACHE: "$[[ inputs.disable_cache ]]"
 nix-ci:build:
   stage: build
   image: registry.gitlab.com/technofab/nix-gitlab-ci/nix-ci:$[[ inputs.image_tag ]]
+  cache:
+    - key:
+        files: $[[ inputs.cache_files ]]
+      paths:
+        - generated-gitlab-ci.yml
+    - key: nix
+      paths:
+        - .nix-cache/
   before_script:
-    - source setup_nix_ci
+    # generated-gitlab-ci.yml exists in the cache
+    - '[ -f "generated-gitlab-ci.yml" ] && export CACHED=true && echo "Using cached pipeline file (skip cache with NIX_CI_SKIP_CACHE)" || true'
+    # allow the user to manually skip the cache (when the key files are not correctly configured etc.)
+    - '[ -n "$NIX_CI_SKIP_CACHE" ] && unset CACHED && echo "Caching skipped for this job (through NIX_CI_SKIP_CACHE)" || true'
+    # only setup when we need to generate the pipeline yaml
+    - 'if [ -z "$CACHED" ]; then source setup_nix_ci; fi'
   script:
-    # build the generated-gitlab-ci.yml
-    - nix build .#gitlab-ci-config
-    - install result generated-gitlab-ci.yml
+    # build the generated-gitlab-ci.yml if it does not exist in the cache
+    - 'if [ -z "$CACHED" ]; then nix build .#gitlab-ci-config && install result generated-gitlab-ci.yml; fi'
   after_script:
-    # upload to binary cache
-    - finalize_nix_ci
+    # NOTE: environment variables of before_script and script don't exist here anymore
+    #
+    # save to binary cache or Gitlab CI cache only if we actually built something
+    #  check if /tmp/nix-store-before exists as $CACHED never exists here and the file only exists if "setup_nix_ci" is called
+    - 'if [ -f "/tmp/nix-store-before" ]; then finalize_nix_ci; fi'
   artifacts:
     paths:
       - generated-gitlab-ci.yml
-
 nix-ci:trigger:
   stage: trigger
   needs:
@@ -35,4 +60,5 @@ nix-ci:trigger:
       - artifact: generated-gitlab-ci.yml
         job: nix-ci:build
     strategy: depend
-
+    forward:
+      pipeline_variables: true